1. Field of the Invention
The present invention is directed to a drive system, and more particularly to a drive system for operating a pair of counter rotating air propellers that propel an airboat.
2. Background Information
Drive systems for propelling airboats are known in the art. For example, U.S. Pat. No. 6,540,570 B1 issued to Eakin on Apr. 1, 2003. This reference illustrates an airboat where the engine is mounted high above the hull. A small compact transmission is driven by the engine through a belt connection located between a drive shaft and a sprocket. A number of gears transmit power from the engine and rotate the air propellers.
Other examples of prior art airboat drive systems include:                (a) U.S. Pat. No. 5,839,926 issued to K-Way on Nov. 24, 1998,        (b) U.S. Pat. No. 6,053,782 issued to Bell on Apr. 25, 2000,        (c) U.S. Pat. No. 6,478,641 issued to Jordan on Nov. 12, 2002,        (d) U.S. Pat. No. 5,724,867 issued to Jordan on Mar. 10, 1998, and        (e) U.S. Pat. No. 6,299,485 issued to Jordan on Oct. 9, 2001.        
All of these references illustrate an engine mounted high above the hull of an airboat. A single compact transmission is driven by a direct connection to the engine through a drive shaft. A number of gears are provided to operate a pair of output drive shafts. One of the output drive shafts is hollow and surrounds the other solid drive shaft to rotate the air propellers.
The prior art airboat drive system references consistently teach mounting an engine high above the hull of an airboat in combination with a single compact transmission. Keeping the engine high and the transmission compact provides the necessary clearance between the tips of the air propellers and the hull of the airboat.
However, there are a number of problems with the prior art airboat drive systems. The transmissions are overly complex with many gears. They require multiple long output drive shafts, including a solid output drive shaft located within a hollow output drive shaft. Mounting the engine and drive system high above the hull creates a high center of gravity. The compactness, and horizontal input and output shafts of these transmissions renders the transmission completely unusable in situations when an engine is mounted low in the hull of an airboat.
Another example of a prior art drive system is shown in the Husky™ Nattiq™ airboat (www.huskyairboats.com). This airboat has the engine mounted low in the hull of an airboat. The existing drive system is an elongated belt extending from a pulley mounted on an end of a drive shaft of an engine to another pulley mounted on a air propeller drive shaft. However, external belt drives are very noisy, prone to wear, and can become dangerous upon failure of the belt.
Other examples of prior art marine drive systems with counter rotating water propellers are also known. These include inboard stern drives and lower units for outboard motors such as:                (a) U.S. Pat. No. 5,890,938 issued to Brunswick on Apr. 6, 1999,        (b) U.S. Pat. No. 5,529,520 issued to Kaisha on Jun. 25, 1996, and        (c) U.S. Pat. No. 5,558,498 issued to Kaisha on Sep. 24, 1996        
However, the marine based prior art solutions also suffer from overly complex transmissions, specific hydrodynamic housings for application in a water environment, and multiple drive shafts (again, a solid drive shaft inside a hollow drive shaft). Assembly of these units is difficult and time consuming. This area of prior art is simply not adaptable to airboats for operating a pair of air propellers.
Therefore, there is a need for a drive system for counter rotating a pair of air propellers when an engine is mounted low in the hull of an airboat.